Thread threadDB = new Thread(delegate() { getDataBase(); });
threadDB.Start();

private void getDataBase()
{
comboBox1.Invoke((MethodInvoker)(() => {   this.TableAdapter.Fill(this.DataSet.Test);}));
}

                
Thread threadDB = new Thread(delegate() { getDataBase(); });
threadDB.Start();

private void getDataBase()
{
this.TableAdapter.Fill(this.DataSet.Test);

comboBox1.Invoke((MethodInvoker)(() =>
                {
                    this.comboBox1.DataSource = this.DataSet.Test;
                    this.comboBox1.DisplayMember = "Name";
                    this.comboBox1.ValueMember = "ID";
                  
                }));
}